Kenneth Martin Williamson

Electrical breakdown phenomena involving material interfaces

Electrical breakdown in a composite gas-solid dielectric is described in qualitative terms. Continuum- and particle-based calculations are performed on idealized structures. The analysis and the calculations suggest that dielectric permittivity has an important role at early times in the breakdown events. The continuum calculations show that the space-charge limited current in the solid dielectric has an important role at longer times. At very long times, the Joule heating from the space-charge limited current is expected to produce thermal breakdown.

Double and single planar wire arrays at high and low impedance university-scale generators

Single Planar Wire Arrays (SPWA) and Double Planar Wire Arrays (DPWA), which consist of one or two parallel rows of wires, respectively, have demonstrated high radiation efficiency (up to 30 kJ), compact size (1.5-3 mm), and usefulness for various applications in experiments on the high-impedance Zebra (1.9Ω, 1 MA, 100 ns). For example, DPWAs are very suitable for the new compact multi-source hohlraum concept, astrophysical applications, and as an excellent radiation source. Their implosion dynamics strongly depends on the critical load parameter, the aspect ratio Φ (width to inter-planar gap Δ) as well as on load wire material and mass. We have studied implosion dynamics and radiative properties of DPWAs at the enhanced Zebra current of 1.5-1.7 MA and have demonstrated the new regimes of implosions with asymmetric jets, no precursor formation, and very early radiation for larger sized (Δ=9 mm, Φ=0.54) and precursor formation and strong “cold” Ka emission for standard sized (Δ=6 mm, Φ=1.28) DPWAs.

High-voltage atmospheric breakdown across intervening rutile dielectrics

The electrical power grid, aircraft, and defense systems are potentially subject to damage from lightning strikes. Surge arresters are high-voltage safety components used to mitigate damage to many critical systems by diverting transient currents to ground via breakdown. Some arresters utilize high-permittivity dielectric materials, such as rutile (TiO2), to ensure breakdown occurs at a prescribed voltage and prevent a transient voltage pulse from affecting downstream components. Though widely used, the physical mechanisms for surface breakdown in surge arresters are not well understood. Electrical discharge experiments are being conducted to help develop predictive computational models of the fundamental processes of surface breakdown in the vicinity of high-permittivity material interfaces. Discharge path imaging and electrical data are presented. Results are compared to electrostatic calculations using an ionization coefficient-based approach and Townsend-breakdown criteria for non-uniform fields and the observed breakdown path. It is shown that rutile reduced the breakdown voltage of an electrode gap by ~50% even when the visible discharge path did not interact directly with the sample.